This invention relates to a selectively controlled dual delivery pump, particularly for motor vehicle application.
As is known, modern motor vehicles, and especially motor cars, are equipped with windshield and rear window washers, while a similar system is gaining increasing acceptance for the headlights. In general, each washing system is supplied by an individual pump which may, however, draw from a common reservoir. This involves significant installation costs, which are sometimes unjustified by the motor vehicle class. for example, rear window washers are indeed required on so-called "two-volume" cars, to which class belong most of "compact" cars.
In order to lower costs, it has been proposed of using a dual delivery pump, wherein selective delivery to either of two different systems, such as the windshield washer and rear window washer, is controlled by the direction of rotation of the pump impeller; the two directions of rotation being obtained by switching the polarity of an impeller drive motor.
A dual delivery, selectively controlled pump of this type is disclosed, as an example, in West Germany Patent Application Ser. No. 30 23 897.2, filed on June 26, 1980. That pump makes use, for selectively switching between two delivery lines, of a changeover shutter rotatively driven by the impeller hub, whereto it is connected via a friction clutch. Depending on the impeller direction of rotation, the shutter is moved to engage by contact with the inlet port. This prior arrangement has several disadvantages, and primarily a poor seal at the shutter, which results in the liquid seeping past it into the cut off manifold to the detriment of the enabled one, and a significant power loss due to dissipation by the friction clutch between the shutter and impeller hub, which brings about a further load loss in useful delivery.
Other prior approaches are based on the principle of utilizing the pressure differential which is established at the inlet end of a pair of tangential manifolds selectively positioned the one in the pressure section of the stator and the other in the suction section thereof on changing the impeller direction of rotation. Such manifolds are cut off by one-way valves the shutter whereof is urged into sealing engagement with its respective valve seat by the action of a spring which is calibrated to the maximum pressure differential value. Even the latter approach shows several drawbacks, and especially a great load loss, which brings about a significant reduction in the useful delivery rate owing to the throttling down introduced by the valves and the preload acting on the valve shutters.